1. Field of the Invention
The disclosed invention is directed to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming that uses multiple laser beams.
2. Discussion of the Background
A high speed printing and a high resolution are increasingly demanded for electrophotographic technology and a multiple laser beam technique has recently been developed as one solution. The multiple laser beam technique typically uses a laser diode array that includes a plurality of laser diodes generally arranged in line in a direction relative to a sub-scanning direction of the laser beams. In practice, the laser diode array is mounted in an optical system in such a way that the laser diode array has an angle smaller than 90xc2x0 relative to a direction corresponding to a main scanning direction of the laser beams. This is to justify a pitch of lines drawn down in a sub-scanning direction on a surface of a writing member (e.g., a photoconductive drum).
In connection with the above-mentioned multiple laser beam technology, several attempts are described in published Japanese unexamined patent applications No. 2000-118038, No. 06-227037, No. 06-300980, and No. 09-174924, for example.
However, the above-mentioned laser diode array has a drawback. That is, when the laser diode array including laser diodes is mounted with a slanting angle, the lines drawn down by the laser beams have an undesired pitch or a displacement in a main scanning direction. To eliminate such an undesired pitch in the main scanning direction, a beam detection for synchronization is required for each of the laser diodes. However, since a distance between any adjacent two of the laser diodes is relatively small, the beam detection for synchronization for each of the laser diodes cannot easily be performed. Therefore, an issue arises as to how to eliminate such an undesired pitch in the main scanning direction.
In addition, this laser diode array having laser diodes with a slanting angle, as described above, involves another drawback. That is, some optical systems may require a reversed slanting direction of laser diodes due to a structural reason, for example. In this case, if a beam detection on a specific laser beam (e.g., typically a laser beam of a channel 1) for synchronization is conducted, this optical system is required to perform a relatively complex control of a synchronization because the channel-1 laser beam of the laser diode array in the reversed slanting direction draws a line at an innermost position in the main scanning direction.
Accordingly, one object of the present invention is to describe a novel image forming apparatus with improvements.
In one example, this novel image forming apparatus includes a light source, a light beam controlling mechanism, a sensor, and a signal controller.
The light source includes a plurality of light emitting elements arranged in line for simultaneously emitting a plurality of parallel light beams. The light source is arranged with an angle smaller than 90xc2x0 relative to a sub-scanning direction of the plurality of parallel light beams. The light beam controlling mechanism is configured to control the plurality of parallel light beams to simultaneously scan a plurality of lines on a surface of a photoconductive member in a main scanning direction. The sensor is configured to detect one of the plurality of parallel light beams and to generate a line synchronous signal upon detecting the one of the plurality of parallel light beams. The signal controller is configured to synchronize and to modulate a plurality of parallel image data streams that respectively drive the plurality of light emitting elements of the light source to emit the plurality of parallel light beams in accordance with the plurality of parallel image data streams.
In this novel image forming apparatus, the controller may include a plurality of FIFOs, a PLL circuit, a frequency divider, a synchronous clock generator, and a plurality of drivers. The plurality of FIFOs are configured to delay the plurality of parallel data streams, respectively. The PLL circuit is configured to generate a PLL clock signal having an integral multiple frequency of a pixel clock signal. The frequency divider is configured to divide the PLL clock signal into a plurality of clock signals having a same frequency and having phases sequentially varied. The synchronous clock generator is configured to select one of the plurality of clock signals having the same frequency and having the phases sequentially varied. The plurality of drivers are arranged and configured to drive the plurality of light emitting elements, respectively, with the one of the plurality of clock signals selected by the synchronous clock generator.
The light source may be a laser diode array including a plurality of laser diodes.
The sensor may arbitrarily be set to detect a predetermined one of the plurality of parallel light beams.
The predetermined one of the plurality of parallel light beams may be a light beam emitted by a light emitting element for scanning a line on the surface of the photoconductive member ahead of other light beams in the main scanning direction.
Another object of the present invention is to describe a novel method of image forming with improvements.
In one example, this novel method of image forming includes the steps of arranging, causing, detecting, inputting, providing, dividing, selecting, separating, delaying, synchronizing, modulating, and driving.
The arranging step arranges a light source with an angle smaller than 90xc2x0 relative to a sub-scanning direction of a photoconductive member. The light source includes a plurality of light emitting elements in line. The causing step causes the plurality of light emitting elements to simultaneously emit a plurality of parallel light beams. The detecting step detects one of the plurality of parallel light beams and generates a line synchronous signal upon detecting the one of the plurality of parallel light beams. The inputting step inputs image data. The providing step provides a PLL clock signal having an integral multiple frequency of a pixel clock signal. The dividing step divides the PLL clock signal into a plurality of pixel clock signals having a same frequency and having phases sequentially varied. The selecting step selects one of the plurality of pixel clock signals having the same frequency and having the phases sequentially varied. The separating step separates the image data into a plurality of parallel data streams. The delaying step delays the plurality of parallel data streams, respectively, with the one of the plurality of pixel clock signals selected in the selecting step. The synchronizing step synchronizes the plurality of parallel image data streams with the one of the plurality of pixel clock signals selected in the selecting step. The modulating step modulates a plurality of driving signals with the plurality of parallel image data streams. The driving step drives the plurality of light emitting elements with the plurality of parallel image data streams, respectively, synchronized in the synchronizing step.
The arranging step may arrange a laser diode array including a plurality of laser diodes.
The detecting step may arbitrarily detect a predetermined one of the plurality of parallel light beams.
The predetermined one of the plurality of light beams may be a light beam emitted by a light emitting element for scanning a line on the surface of the photoconductive member ahead of other light beams in the main scanning direction.